Substance II is known as a selective blocker of α1C receptors, which allows for its use for treating problems with retention of urine in connection with hyperplastic prostate without influencing blood pressure. This property differentiates the substance from a number of other blockers of α1C receptors that do not act selectively and, therefore, exhibit side effects in the form of hypotension connected with various unpleasant conditions of the patient (for example EP 710 486).
A mixture of the (R) and (S) enantiomers of 5-[2-[2-(2-ethoxyphenoxy)ethylamino]propyl]-2-methoxybenzenesulfonamide (thereinafter racemic tamsulosin) was described in patent EP 34 432. The method of preparation of the group of sulfamoyl-phenylethylamine derivatives claimed in the patent consisted in reductive amination (or amination with subsequent reduction) of ketones of type III

The group of substances described in patent EP 34 432 was characterized by the property to block α adrenergic receptors, which makes them suitable agents for treatment of a number of diseases, especially hypertension, congestive heart failure or problems connected with urinary tract.
Later, it turned out that the above mentioned substance II, especially the (R)-enantiomer, exhibits selective effect during treatment of problems connected with hyperplastic prostate without influencing blood pressure or heart action (Honda K. and Nakagawa C: Alpha-1-adrenoreceptor antagonist effect of optical isomers YM-12617 in rabbit lower urinary tract and prostate—J. Pharm Exp. Ther. 239, 512, (1986)).
This led to attempts at effective synthesis of optically active substance II.
In the Austrian patent AT 397960, the synthesis of (R)-tamsulosin (II) is solved by reaction of optically active amine of formula I
with brominated ether of formula IV

The synthesis turned out to be very advantageous if the starting amine I was prepared according to the method described in patent EP 257785, or divisional EP 380144.
The patents describe the path indicated in the following scheme:

Reaction of ketone III with (R)-α-methylbenzylamine in a reductive environment under catalysis of PtO2 results in optically active (R,R)-diastereoisomer V with high optical purity (around 92%). This intermediate product is further re-crystallized to obtain high optical purity and converted, by hydrogenolysis, to optically active (R)-hydrochloride VI. The latter is converted to the (R)-amine of formula I itself by action of a base.
However, a reproduction of this procedure has shown that the yield of R amine I ranges between 10 and 15% and that of resulting tamsulosin II even only about 4 to 5% of the theory. The yield of the last stage of the synthesis, i.e. preparation of the substance II from the substance I, was significantly improved according to patent CZ 291802. However, there is still the problem of very low yield of the important intermediate I.
However, surprisingly, such a method has now been found out that can produce even higher than twofold yield.